Low temperature oxydehydrogenation of ethane to ethylene has become well known since the publication of "The Oxidative Dehydrogenation of Ethane over Catalyst Containing Mixed Oxide of Molybdenum and Vanadium" by E. M. Thorsteinson, T. P. Wilson, F. G. Young and P. H. Kasai, Journal of Catalysis 52, pp. 116-132 (1978). This article discloses mixed oxide catalysts containing molybdenum and vanadium together with another transition metal oxide (Ti, Cr, Mn, Fe, Co, Ni, Nb, Ta, or Ce). The catalysts are active at temperatures as low as 200.degree. C. for the oxydehydrogenation of ethane to ethylene.
The effectiveness of the oxydehydrogenation of ethane to ethylene is usually primarily determined by two parameters: conversion of ethane, and selectivity (efficiency) to ethylene. As used herein, these terms are defined as follows: ##EQU1## wherein: [ ]=relative moles of the component and the production of acetic acid is negligible. The terms in the art are sometimes calculated differently but the values calculated either way are substantially the same.
Under certain reaction conditions, substantial amounts of acetic acid can be formed as a co-product and the effectiveness of the reaction to ethylene and acetic acid is calculated by the following equations: ##EQU2##
U.S. Pat. No. 4,250,346 discloses catalytic oxydehydrogenation of ethane to ethylene at temperatures less than 550.degree. C. in which the catalyst is a calcined composition comprising the elements Mo, X, and Y in the ratio EQU Mo.sub.a X.sub.b Y.sub.c
wherein:
X=Cr, Mn, Nb, Ta, Ti, V, and/or W PA1 Y=Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Tl, and/or U PA1 a=1 PA1 b=0.05 to 1.0 PA1 c=0 to 2 PA1 X=nothing or at least one of the following : Li, Sc, Na, Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, Y, Ta, Cr, Fe, Co, Ni, Ce, La, Zn, Cd, Hg, Al, Tl, Pb, As, Bi, Te, U, Mn, and W; and PA1 a=0.5 to 0.9 PA1 b=0.1 to 0.4 PA1 c=0.001 to 0.2 PA1 d=0.001 to 0.1 PA1 e=0.001 to 1.0
The numerical values of a, b, and c represent the relative gram-atom ratios of the elements Mo, X, and Y, respectively, which are present in the catalyst composition. The elements Mo, X, and Y are present in the catalyst composition in combination with oxygen.
Generally, the process of preparing the catalyst used in the patent includes forming a precursor solution of the compounds of the selected metals. This solutions is usually dried to obtain a solid which is broken up and calcined to form oxides. In Example 35, the precursor solution was filtered, allowed to stand three days, and then filtered again. The resulting filtrate was dried and processed to produce a catalyst. The catalyst was tested as a neat catalyst without a support.
None of the prior art has disclosed or suggested the surprising advantages of using a support for the filtrate. It is well known that catalyst performance can be reduced by the presence of a support as can be seen from Examples 36 and 37 of the patent. The same catalyst used with a support in Example 37 performed extremely poorly as compared to the neat catalyst used in Example 36.